In general, as a representative large-scale display, a liquid crystal display (LCD) or a plasma display panel (PDP) is used.
Differently from the PDP of a self-emitting type, the LCD essentially requires a separate backlight unit due to absence of self-emitting light emitting devices.
Backlight units used in LCDs are classified into an edge type backlight unit and a direct type backlight unit according to positions of light sources. In the edge type backlight unit, light sources are disposed on left and right side wall parts and/or upper and lower side wall parts of an LCD panel and a light guide plate is used to uniformly distribute light throughout the overall surface of the LCD panel, and thus uniformity of light is improved and the panel has an ultra-thin thickness.
In the direct type backlight unit which is generally used in displays having a size of 20 inches or more, a plurality of light sources is disposed under a panel. Thus, the direct type backlight unit has excellent optical efficiency, as compared to the edge type backlight unit, thereby being mainly used in large-scale displays requiring high brightness.
As light sources of the conventional edge type or direct type backlight unit, cold cathode fluorescent lamps (CCFLs) are used. However, a backlight unit using CCFLs may consume a considerable amount of power because power is applied to the CCFLs at all times, exhibit a color reproduction rate of about 70% that of a CRT, and cause environmental pollution due to addition of mercury.
In order to solve these problems, research into a backlight unit using light emitting diodes (LEDs) has been conducted now.
If LEDs are used as the backlight unit, an LED array may be partially turned on/off and thus power consumption may be considerably reduced. Particularly, RGB (red, green and blue) LEDs exceed 100% of national television system committee (NTSC) color reproduction range specifications, thus providing a more vivid image to consumers.
Further, LEDs fabricated using a semiconductor process are harmless to the environment.
LCD products employing the LEDs having the above advantages have entered the market recently, but these products have a driving mechanism differing from the conventional CCFL light source and thus a driver and a printed circuit board thereof are expensive. Therefore, the LED backlight unit has been applied only to expensive LCD products.